1. Field of the Invention
The present invention relates to an optical disk(disc) recording/reproducing apparatus for recording and reproducing a signal on and from a disk(disc)-shaped record medium or an optical disk reproducing apparatus, and more particular to a disk type determining apparatus used in such an apparatus, an optical disk reproducing apparatus which can change an operational condition in accordance with the determined disk type, and a tracking error signal generating apparatus used in such a disk reproducing apparatus.
2. Description of the Related Art
Generally, in this type of an information reproducing apparatus, a tracking control and a focus control for an optical head are performed so as to accurately write or read data when recording or reproducing. Such controls are performed by controlling the optical head by means of a so-called servo control circuit. Typically, a three-beam method and a phase difference method (a phase difference detecting method: a DPD (Differential Phase Detect) method) are actually used as a method of generating a tracking error signal used in the tracking control for the optical head. These methods are described in, for example, "Compact Disk Reader" edited by Ohm Company, page 134-138 (1982) and Japanese Patent Application Laid-open (KOKAI) No.61-230637 Gazette. Various types are developed as a disk-shaped optical record medium. A plurality of types, such as a CD-ROM, a video CD, a DVD (Digital Versatile Disk) and the like, are actually used in addition to a so-called CD (Compact Disc), as a disk having a diameter of 12 cm. Although data formats, compression manners, data record densities for the recorded information are various in these disks, all of diameters are 12 cm. Moreover, data can be read out by the optical head (optical pickup). Thus, a reproducing apparatus which can be used in several types of disks is developed. A utilization of a two-focus type of an optical head is proposed in order to implement a plural use reproducing apparatus for a single-layer type, a two-layer type and a phase variation type for recording and reproducing, as CD having a thickness of 1.2 mm and DVD in which two layers (each has a thickness of 0.6 mm) are pasted together.
In a case of using such a two-focus type of an optical head, unless an appropriate focus position is found out by a so-called focus search and then a focus servo control is turned on, a disk type can not be determined. In the plural use reproducing apparatus, respective parameters and the like for a signal processing circuit are suitably selected and set in accordance with the disk type. Thus, if the determination of the disk type is not finished, reproduction of data on the disk can not be started. Hence, it takes a long time to start the reproduction.
On the other hand, when considering the dual use reproducing apparatus for CD having a thickness of 1.2 mm and DVD having a thickness of 0.6 mm, the three-beam method is optimal for the CD as a method of generating the tracking error signal. However, when applying this three-beam method to the DVD, a signal of a layer that is not targeted is leaked into especially in a case of the two-layer DVD, and then this results in a problem. Moreover, in the three-beam method, a cross talk from adjacent tracks results in a problem in a case of a land group record of recording on a phase variation medium at a high density. The phase difference method is suitable for the DVD. However, when a light spot is small at a time of applying to the CD, a wave of the tracking error signal does not become a sine wave. Thus, this may result in a problem at a time of a track cross. And, in the phase difference method (Differential Phase Detect method), a quality of the tracking error signal may be deteriorated by a depth of a bit. Furthermore, when using a two-lens type of an optical pickup, unless turning on the focus servo control and then reading out a signal from a disk, the disk type can not be determined. Hence, it takes a long time to start the reproduction.